Palladium and gold catalysts for sustainable chemical processing

The main focus of this thesis is the investigation of sustainable routes for the production of commercially important higher and functionalised aliphatic and aromatic amines through the application of (oxide and carbon) supported palladium and gold catalysts. In the hydrogenation of butyronitrile as a model aliphatic nitrile, unsupported Pd promoted the formation of primary and secondary amines. The acid-base character of the support and available surface reactive hydrogen are critical catalyst variables. The greater acidity of Pd/C (relative to Pd/Al2O3) resulted in the predominant formation of the tertiary (tributyl-) amine where spillover hydrogen serves to elevate hydrogenation rate. The combination of Ba with Pd (supported bimetallic) proved effective in promoting hydrogenation activity with 100% selectivity to the secondary amine, which is attributed to a decrease in acidity and modification to Pd dispersion that enhances surface hydrogen. The feasibility of an alternative route for the synthesis of higher aliphatic secondary and tertiary amines from primary and secondary amine feedstock has been demonstrated. Control of contact time is key where the use of a multiple catalyst beds in series facilitates higher yields. This is accounted for in terms of surface reaction mechanism. This configuration was also efficient for the synthesis of benzylamine from benzonitrile. Hydrogenation selectivity was further assessed by considering the reduction of functionalized nitroarenes (p-chloronitrobenzene (p-CNB) and p-nitrobenzonitrile (p-NBN)). It is shown that the redox nature of the support has a direct impact on the activity and selectivity response. The formation of Pdδ+ (on carbon) activates the nitro group with subsequent C-Cl bond scission with the formation of p-chloroaniline (p-CAN) and aniline (AN). The occurrence of Pdδ- (on SiO2 and Al2O3) favours interaction via the aromatic ring that activates both –NO2 and –Cl for attack generating AN and nitrobenzene. The formation of a PdZn alloy (established by XPS analysis) in addition to Pd0 selectively activates the –NO2 group and promotes the sole formation of p-CAN at all levels of conversion (and close to 100%). Exclusive conversion of p-NBN to p-aminobenzonitrile was achieved over a series of oxide (CeO2, Fe2O3, Fe3O4, TiO2, ZrO2 and Al2O3) supported (1 mol %) Au catalysts. Hydrogen uptake is structure sensitive and favoured by smaller nano-scale metal particles with a consequent increase in activity. Reaction over Au/TiO2 delivered the highest specific hydrogenation rate, which is explained on the basis of –NO2 activation at the metal-support interface that is facilitated by Nδ+ interaction with electron rich gold (Auδ-, demonstrated by XPS). This effect is shown to extend to TiO2 supported Ag and Pd. Supported Au is also effective in the selective hydrogenation of benzaldehye in liquid phase operation using water as a green solvent. 100% yield of the target benzyl alcohol was attained over Au/Al2O3 whereas Pt/Al2O3 generated toluene and benzene as significant (hydrogenolysis) by-products. Solvent effects were evaluated where a direct correlation between selective hydrogenation rate and dielectric constant is demonstrated and ascribed to competitive adsorption, which was more severe for less polar alcohol solvents. Solvation by polar water facilitated benzaldehyde activation. The same activity and selectivity trends were found to also apply to continuous gas phase reaction. The results presented in this thesis demonstrate, for the first time, direct participation of the support in the catalytic hydrogenation of aliphatic nitriles over Pd-based catalysts. This can be harnessed to enhance amine production in a sustainable continuous flow gas operation process. Moreover, secondary and tertiary aliphatic amines can be selectively produced from the correspondent primary and secondary amines over Pd in continuous mode. The use of reducible supports can result in the formation of an alloy phase and surface defects with beneficial selectivity and activity effects in the production of functionalized amines. The selective catalytic action of supported Au catalysts has been established in achieving 100% yield of benzyl alcohol (from benzaldehyde) using water as a benign solvent

Population response of intestinal microbiota to acute Vibrio alginolyticus infection in half-smooth tongue sole (Cynoglossus semilaevis)

IntroductionVibriosis causes enormous economic losses of marine fish. The present study investigated the intestinal microbial response to acute infection of half-smooth tongue sole with different-dose Vibrio alginolyticus within 72 h by metagenomic sequencing.MethodsThe inoculation amount of V. alginolyticus for the control, low-dose, moderate-dose, and high-dose groups were 0, 8.5 × 101, 8.5 × 104, and 8.5 × 107 cells/g respectively, the infected fish were farmed in an automatic seawater circulation system under a relatively stable temperature, dissolved oxygen and photoperiod, and 3 ~ 6 intestinal samples per group with high-quality DNA assay were used for metagenomics analysis.ResultsThe acute infections with V. alginolyticus at high, medium, and low doses caused the change of different-type leukocytes at 24 h, whereas the joint action of monocytes and neutrophils to cope with the pathogen infection only occurred in the high-dose group at 72 h. The metagenomic results suggest that a high-dose V. alginolyticus infection can significantly alter the intestinal microbiota, decrease the microbial α-diversity, and increase the bacteria from Vibrio and Shewanella, including various potential pathogens at 24 h. High-abundance species of potential pathogens such as V. harveyii, V. parahaemolyticus, V. cholerae, V. vulnificus, and V. scophthalmi exhibited significant positive correlations with V. alginolyticus. The function analysis revealed that the high-dose inflection group could increase the genes closely related to pathogen infection, involved in cell motility, cell wall/ membrane/envelope biogenesis, material transport and metabolism, and the pathways of quorum sensing, biofilm formation, flagellar assembly, bacterial chemotaxis, virulence factors and antibiotic resistances mainly from Vibrios within 72 h.DiscussionIt indicates that the half-smooth tongue sole is highly likely to be a secondary infection with intestinal potential pathogens, especially species from Vibrio and that the disease could become even more complicated because of the accumulation and transfer of antibiotic-resistance genes in intestinal bacteria during the process of V. alginolyticus intensified infection

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Selective gas phase hydrogenation of p-nitrobenzonitrile to p-aminobenzonitrile over zirconia supported gold

The catalytic action of Au/ZrO2 in the gas phase hydrogenation of p-nitrobenzonitrile (p-NBN) to p-aminobenzonitrile (p-ABN) has been assessed against Au/Al2O3. Crystalline ZrO2 was prepared by precipitation of ZrOCl2 with aqueous NH3 and calcined to generate tetragonal and monoclinic phases. Catalyst and support were characterised by surface area/porosity, temperature-programmed reduction (TPR), H2 chemisorption/temperature programmed desorption (TPD), X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) measurements. Higher calcination temperatures (673–973 K) increased the monoclinic ZrO2 content with a decrease in surface area and pore volume. Introduction of Au by deposition–precipitation resulted in tetragonal → monoclinic transformation with post-TPR formation of Au particles in the 3–13 nm size range and electron transfer from ZrO2. Reaction over Au/ZrO2 delivered 100% p-ABN yield with higher turnover frequency (267 h−1) than Au/Al2O3 (109 h−1) attributed to greater H2 chemisorption capacity under reaction conditions and enhanced −NO2 activation. Au/ZrO2 outperformed benchmark Pd/Al2O3 and Ni/Al2O3, which generated p-aminotoluene via subsequent hydrogenation/hydrogenolysis

Gas phase chemoselective hydrogenation of p-nitrobenzonitrile over gold:effect of metal particle size, support and the metal-support interface

We report the catalytic gas phase hydrogenation of p-nitrobenzonitrile (p-NBN) to p-aminobenzonitrile (p-ABN) over a series of oxide (CeO2, Fe2O3, Fe3O4, TiO2, ZrO2 and Al2O3) supported (1 mol%) Au catalysts (mean size 3–8 nm from electron microscopy). Hydrogenation rate was structure sensitive with lower turnover frequencies (TOF) over larger Au nanoparticles in the 4–8 nm interval and a decrease in TOF for Au ≤ 3 nm. This size dependence also applies to H2 chemisorption under reaction conditions. Rate normalised with respect to H2 uptake showed a dependence on support redox potential where the formation of oxygen vacancies (from O2 titration) served to stabilise the −NO2 group, lowering reactivity. Reaction over Au/TiO2 with modified electronic character (from XPS) deviated from this trend and delivered the highest specific hydrogenation rate, which is attributed to –NO2 activation at the Au-TiO2 interface; this effect extends to TiO2 supported Ag and Pd

Gas phase chemoselective hydrogenation of p

We report the catalytic gas phase hydrogenation of p-nitrobenzonitrile (p-NBN) to p-aminobenzonitrile (p-ABN) over a series of oxide (CeO2, Fe2O3, Fe3O4, TiO2, ZrO2 and Al2O3) supported (1 mol%) Au catalysts (mean size 3–8 nm from electron microscopy). Hydrogenation rate was structure sensitive with lower turnover frequencies (TOF) over larger Au nanoparticles in the 4–8 nm interval and a decrease in TOF for Au ≤ 3 nm. This size dependence also applies to H2 chemisorption under reaction conditions. Rate normalised with respect to H2 uptake showed a dependence on support redox potential where the formation of oxygen vacancies (from O2 titration) served to stabilise the −NO2 group, lowering reactivity. Reaction over Au/TiO2 with modified electronic character (from XPS) deviated from this trend and delivered the highest specific hydrogenation rate, which is attributed to –NO2 activation at the Au-TiO2 interface; this effect extends to TiO2 supported Ag and Pd